How dandruff could help to collar a criminal

Criminals with dry skin or itchy scalp should look for a new profession: scientists can now build a DNA `fingerprint', from a single speck of dandruff. Esther Leach reports on how the breakthrough follows two years of work.

It is now possible to use a single cell to confirm a person's unique genetic "fingerprint", according to Dr Ian Findlay, a Leeds pathologist. Presently, forensic scientists need at least 500 cells to generate a DNA profile detailed enough to stand up in court.

Dr Findlay said: "A human cell left on a cigarette butt, a licked stamp or a single sperm can lead to the identity of a suspected criminal. The breakthrough made with the use of computer enhancements of DNA markers will revolutionise forensic science and crime detection. It means even a smudged fingerprint which would normally be of no use to police in the hunt for a criminal suspect can be analysed to obtain a DNA profile.

"In the case of multiple rape, for example, each individual involved can be identified even if the cells are mixed together. Cells left on clothing, even if it has been washed, can be examined and DNA identification still be made using this technique.

"It is possible to conceive of there being no scientific barrier to the detection of crime. There is more work to be done to perfect the technique but this is the breakthrough we have been waiting for."

The development, reported today in the science journal Nature, follows two years of research at the University of Leeds, which has been working closely with Birmingham Forensic Science Service.

A single cell is chosen, and using a technique called Short Tandem Repeat Profiling, which focuses on repeated sequences of combinations of the four DNA "bases" (known as A, T, C and G) within individuals' genes. These "tandem repeats" are inherited and so are strongly tied to a person's heritage. Using computer enhancement reveals the markers which identify an individual's unique genetic make-up.

Results can be available within six hours, giving six "markers" from the DNA, as well as the person's sex. The chance of two unrelated people sharing the same markers and sex is 100 million to 1. British courts will accept DNA evidence with four markers.

In tests so far, the six set of markers can be identified in 50 per cent of single cell samples. Four markers can be identified in another 14 per cent of the samples.

Dr Findlay hopes forensic scientists will be using the technique within a couple of years. A spokesman for the Forensic Science Service, which pioneered the use of DNA profiling, and set up the world's first national criminal intelligence DNA database, said: "This is a crucial breakthrough. It means we can take evidence from smaller samples than ever before."